Floor coverings or wall covering are made essentially based on vinyl chloride homopolymers or copolymers. In addition to its physical and mechanical properties, the use of PVC is advantageous on account of its ease and diversity of use, especially by:
calendering or extrusion for the manufacture of sheets, PA1 coating with plastisol. PA1 hot-bonding to metal surfaces, PA1 corrosion of the tools for the transformation, PA1 degassing, PA1 grinding, PA1 safety, PA1 limited choice of precursor, with regard to the acceptable melt index values.
The inclusion of a swelling agent in the formulations allows foams to be obtained. These can be inhibited by localized printing to obtain relief effects.
However, for reasons associated with environmental protection, studies are currently under way in an attempt to replace PVC by polymers containing neither chlorine nor nitrogen.
Patents DE-3,903,670 C1 and DE-3,903,669 C1 describe the manufacture of floor coverings or wall coverings from PMMA, which is plasticized, by calendering or coating with plastisols.
These products contain a high level of plasticizers and can thus have drawbacks resulting from their migration and their volatility. Furthermore, acrylic compounds are relatively expensive polymers.
Patent application BE-09300955 describes the manufacture of a floor covering on EVA foam by calendering or extrusion and coated with a sheet of a so-called ionomeric compound, extruded as a wear layer. As a result of its excellent properties (transparency, resistance to abrasion, to scratching and to marking), this type of wear layer is considered to be particularly advantageous.
The manufacture of ionomers is itself described in the document "Ionic Polymers", Encyclopedia of Polymer Science and Engineering, Wiley-Interscience, Volume 8 (1987), pp. 393-423.
An ionomer is generally produced in two steps: the manufacture of a precursor, followed by its neutralization with a metal salt.
In order to obtain the precursor, ionic polymers are usually prepared by copolymerization of a functionalized monomer and of an olefinic monomer or by direct functionalization of a pre-existing polymer. Typically, the presence of a carboxyl group is obtained by copolymerization of acrylic acid or methacrylic acid with ethylene, styrene or other monomers. The resulting copolymer contains free acid functions which can be neutralized to the desired degree with metal hydroxides, metal acetates or salts.
The second step consists in neutralizing the said groups. Several routes can be used.
In the reaction in solution, this involves dissolving the copolymer, neutralizing in solution, precipitating it, washing it and finally drying it. The ionomer obtained is then stored with a desiccant to avoid any uptake of moisture.
This method of production is described in the literature, for example: "Ionomers: the sodium salt of Poly(ethylene-co-Methacrylic Acid)", Keling Han and H. Leverne Williams, Journal of Applied Polymer Science, Vol. 38, pp. 73-86 (1989), and U.S. Pat. No. 5,003,012.
The reaction for extrusion-neutralization is carried out in the extrusion die during melting of the products. The temperatures reached in the die are from about 180.degree. C. to 260.degree. C., and sometimes even higher. The sources of cations which can be used are especially Na.sub.2 CO.sub.3, K.sub.2 CO.sub.3, Mg(OH).sub.2, ZnO and Cu(CH.sub.3 COO).sub.2.
During this reaction, volatile products are eliminated in a degassing chamber on the die. This degassing step is very intricate since, with ionomer precursors with a high fluidity index, it is the product which escapes. This technique thus limits the manufacture of ionomer from precursors having an excessively high melt index.
Furthermore, this technique gives rise to contact between melting material and metal surfaces. On account of their chemical composition (presence of acidic sites), these products are corrosive, and it is necessary to work with metal surfaces which have undergone an anticorrosion treatment. If this is not the case, the ionomer causes abrasion of the apparatus for the conversions, by corrosion. In this technique, it is also necessary to limit the moisture, since the synergism between acid, water and high temperature promotes corrosion.
This production technique is described in patent EP-0,537,487 A1.
It is possible to neutralize a precursor film by immersion, by submerging it in a neutralizing solution for a certain period. The degree of neutralization is then adjusted by the residence time in the solution. This technique is itself also followed by a drying period in order to remove any moisture.
An illustration of this technique is given in the publication "Dynamic Mechanical Studies of Partially Ionized and Neutralized Nafion Polymers", Thein Kyu, Mitsuaki Hashiyama and Adi Eisenerg. Can. J. Chem. 61, 680 (1983).
These various techniques, and especially the second, make it possible to obtain ionomeric films. Their good behavior with regard to resistance to abrasion, to scratching and to marking, as well as their transparency, allow them to be used as wear layers in floor coverings. However, adhesion difficulties are observed with the sub-layers or the support, and especially problems of bonding to the metal parts of the complexing tools. On account of their chemical composition, working these films with hot tools (cylinder) results in bonding. The term "hot tack" is used in this case. As regards, the adhesion problems, the solutions envisaged to date are mainly the application of such films using agents of the "hot-melt" type or coating with adhesives. These solutions are the subject of the published patent applications WO 95/11333 and WO 95/08593.
One solution for circumventing the implementation drawbacks, and mainly the "hot tack" drawback, is the use of ionomers in the form of ionomeric powders. This choice would make it possible to avoid the problems of bonding on a cylinder while at the same time obtaining the fusion of a transparent film as a wear layer. However, on account of its chemical composition (presence of ionic bonding), an ionomer has a much higher cohesion energy than the precursor (hydrogen bonding), which makes it very difficult to grind. Cryogenic grinding is thus necessary, but this technique is very expensive and remains very intricate on account of the cold-temperature behavior of the ionomers. Furthermore, the use of powders obtained by these techniques does not consist merely of advantages, since the risks of explosion increase as the fineness of the powder increases. The reason for this is that electrical charges accumulate and the risks of sparks are thus increased. Precautions must consequently be envisaged.
It has already been proposed to produce ionomeric resins by the technique of mixing two dry powders.
In document DATABASE WPI, Section Ch, Week 8651; Derwent Publications Ltd., London, GB; Class A18, AN 86-336142 and JP-A-61 252 204 (MITSUBISHI PETROCH KK), Nov. 10, 1986, it is proposed to prepare a homogeneous dispersion of alpha-olefinic copolymers containing .alpha.,.beta.-unsaturated carboxylic acids and at least one crosslinking agent in powder form chosen from the hydroxides of metals from groups IIa and IIb, followed by blending in the molten state. This technique avoids the use of blenders treated against corrosion.
In document U.S. Pat. No. 4,638,034, ethylene/acrylic acid copolymers or salts thereof are saponified in the molten state in the absence of solvents or water, other than the alkanol by-product. It is also sought to avoid corrosion of the plants.
In document U.S. Pat. No. 5,036,134 an ionomeric precursor of the styrene/acrylate type and an organozinc salt are dry-ground and then mixed in the molten state in a Brabender mixer, cooled with water. The product is used as a binder in paints.
Lastly, document U.S. Pat. No. 3,755,219 proposes to mix, by vigorous stirring, an essentially dry heteropolymer of styrene/maleic anhydride, methyl maleate with a sodium hydroxide solution.
According to a variant, a dry styrene/maleic anhydride copolymer is mixed vigorously and neutralized with ammonia gas.
The interpolymers obtained are used as binders for pigments or adhesives or for coating paper, cardboard or similar materials with pigments, in conjunction with starches or protein materials for coating paper.